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If Biftu gives me a penny, I will have twice as many pennies as he has. If I give Biftu a penny, he and I will have a total of  15 pennies. How many pennies do I currently have?

 Feb 11, 2021
 #1
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+1

You have 9    B has 6

 Feb 11, 2021
 #2
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+1

Let  the  number  of pennies you  have  = x

Let  the  number of pennies that  Bill has  = y

 

So   x +  y   = 15     (1)  

And   (x + 1)   =  2 ( y   -1)   ⇒  x + 1  =  2y  - 2  ⇒  x  =  2y   -  3    (2)

 

Sub (2)  into (1)    and we  get that

 

2y  - 3  +  y   =  15

3y  =  18

y  = 6     =  the  number Bill has

x + 6  =  15

x = 9   =  the number you  have

 

 

cool cool cool

 Feb 11, 2021

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